How to use KX_CharacterWrapper.walkDirection
The wraper.walkDirection is a property of type Vector and not a function so you should do an assignment :

wraper.walkDirection = direction


to move in the local space orientation multiply the direction vector by the orientation matrix of the object :

direction = own.orientation*Vector((0, 0.1, 0))


you should include the Vector type by adding this line :

from mathutils import Vector